Coding apparatus, decoding apparatus, coding-decoding apparatus for video signals, and optical disks conforming thereto

Abstract

A coding and decoding apparatus is used to code and decode video signals. Input video signals are enhanced by an emphasis circuit having a nonlinear characteristic increasing an enhancement degree as amplitude of the input video signal decreases. The enhanced video signal, outputted from the emphasis circuit, is compression coded in an encoder and a code stream, representing a compression coded video signal, is outputted from the encoder. The code stream is transmitted to a decoder and the decoder decodes the code stream, outputting a decoded video signal. The decoded video signal is fed to a de-emphasis circuit having a nonlinear characteristic increasing a suppression degree as amplitude of the input signal decreases. As a result, low noise high quality video signals is reproduced from the de-emphasis circuit.

What is claimed is: 
     
       1. A video signal coding and decoding apparatus, comprising: emphasis means, having a nonlinear characteristic for increasing degree of signal enhancement of said video signal as amplitude of said video signal decreases, and for setting degree of signal enhancement at a desired level and for generating an output signal,   coding means for generating a code row by compression coding the output signal from the emphasis means   decoding means for decoding the code row and for generating a decoded video signal, and   de-emphasis means having a nonlinear characteristic for increasing degree of signal suppression of said decoded video signal as amplitude of said decoded video signal decreases, and for reproducing said video signal by suppressing the decoded video signal, wherein the emphasis means comprises:   means for extracting high frequency components from said video signal;   first limiter means for passing an original amplitude when the magnitude of the high frequency components is not more than a first specified level L1, and limiting the output amplitude of L1 when the magnitude of the high frequency components is more than L1;   first multiplying means for multiplying the output signal of the first limiter means by a first coefficient X1; and   means for adding the output signal of the first multiplying means to the input signal; and   wherein the de-emphasis means comprises:   means for extracting high frequency components of the decoded video signal;   second limiter means for passing respective original amplitudes when the respective magnitudes of the high frequency components of the decoded video signal is not more than a second specified level L2 given in a form of (1+X1)×L1, and limiting the respective output amplitudes to L2 when the magnitude of the respective high frequency components is more than L2;   second multiplying means for multiplying the output signal of the second limiter means by a second coefficient X2; and   means for subtracting the output signal of the second multiplying means from the coded video signal.   
     
     
       2. A video signal coding and decoding apparatus, comprising: emphasis means, having a nonlinear characteristic for increasing degree of signal enhancement of said video signal as amplitude of said video signal decreases, and for setting degree of signal enhancement at a desired level and for generating an output signal,   coding means for generating a code row by compression coding the output signal from the emphasis means   decoding means for decoding the code row and for generating a decoded video signal, and   de-emphasis means having a nonlinear characteristic for increasing degree of signal suppression of said decoded video signal as amplitude of said decoded video signal decreases, and for reproducing said video signal by suppressing the decoded video signal, wherein the emphasis means possesses a frequency characteristic having a peak near fs/4 wherein fs is sampling frequency, and the de-emphasis means possesses a frequency characteristic having a peak near fs/2.   
     
     
       3. A video signal coding and decoding apparatus, comprising: emphasis means, having a nonlinear characteristic for increasing degree of signal enhancement of said video signal as amplitude of said video signal decreases, and for setting degree of signal enhancement at a desired level and for generating an output signal,   coding means for generating a code row by compression coding the output signal from the emphasis means   decoding means for decoding the code row and for generating a decoded video signal, and   de-emphasis means having a nonlinear characteristic for increasing degree of signal suppression of said decoded video signal as amplitude of said decoded video signal decreases, and for reproducing said video signal by suppressing the decoded video signal, further comprising:   means for detecting the amplitude of the video signal for a specific period before enhancing the signal;   means for selecting one of plural types of mode signals depending on the amplitude detected by the detecting means;   first level control means for controlling the amplitude of the video signal by the mode signal selected by the selecting means; and   second level control means for controlling the amplitude of the reproduced video signal, after the signal is suppressed in a reverse characteristic of the first level control means.   
     
     
       4. A video signal coding and decoding apparatus, comprising: emphasis means, having a nonlinear characteristic for increasing degree of signal enhancement of said video signal as amplitude of said video signal decreases, and for setting degree of signal enhancement at a desired level and for generating an output signal,   coding means for generating a code row by compression coding the output signal from the emphasis means   decoding means for decoding the code row and for generating a decoded video signal, and   de-emphasis means having a nonlinear characteristic for increasing degree of signal suppression of said decoded video signal as amplitude of said decoded video signal decreases, and for reproducing said video signal by suppressing the decoded video signal, wherein the emphasis means comprises:   means for comparing the amplitude of the video signal with a specific amount: and   means for enhancing the video signal by a equivalent enhancement degree to the signal suppression degree of the de-emphasis means when the amplitude of the video signal is not more than the specific amount, and enhancing the video signal by a lower enhancement degree than the signal suppression degree of the de-emphasis means when the amplitude of the video signal is more than the specific amount.   
     
     
       5. A video signal coding and decoding apparatus, comprising: emphasis means, having a nonlinear characteristic for increasing degree of signal enhancement of said video signal as amplitude of said video signal decreases, and for setting degree of signal enhancement at a desired level and for generating an output signal,   coding means for generating a code row by compression coding the output signal from the emphasis means   decoding means for decoding the code row and for generating a decoded video signal, and   de-emphasis means having a nonlinear characteristic for increasing degree of signal suppression of said decoded video signal as amplitude of said decoded video signal decreases, and for reproducing said video signal by suppressing the decoded video signal, wherein the emphasis means comprises:   vertical emphasis means for enhancing the signal amplitude to a vertical direction of a screen; and   horizontal emphasis means for enhancing the signal amplitude by a greater signal enhancement degree than the signal enhancement degree of the vertical emphasis means to a horizontal direction of the screen; and   wherein the de-emphasis means comprises:   vertical de-emphasis means for suppressing the signal amplitude to the vertical direction of the screen; and   horizontal de-emphasis means for suppressing the signal amplitude by a greater signal suppression degree than the signal suppression degree of the vertical de-emphasis means to the horizontal direction of the screen.   
     
     
       6. A video signal coding and decoding apparatus, comprising: emphasis means, having a nonlinear characteristic for increasing degree of signal enhancement of said video signal as amplitude of said video signal decreases, and for setting degree of signal enhancement at a desired level and for generating an output signal,   coding means for generating a code row by compression coding the output signal from the emphasis means   decoding means for decoding the code row and for generating a decoded video signal, and   de-emphasis means having a nonlinear characteristic for increasing degree of signal suppression of said decoded video signal as amplitude of said decoded video signal decreases, and for reproducing said video signal by suppressing the decoded video signal,   mode changeover means for issuing a mode signal by selecting one of L modes wherein L is a natural number greater than one:   whereby the emphasis means enhances the signal amplitude by a signal enhancement degree defined by the mode signal, and the de-emphasis means suppresses the signal amplitude by a signal suppression degree of complimentary characteristic to the signal enhancing characteristic of the emphasis means of the greatest enhancement degree among the L modes.   
     
     
       7. A coding and decoding apparatus of claim 6, further comprising: means for recording or transmitting the mode signal together with the coded video data; and   means for reproducing the recorded or transmitted mode signal;   whereby the de-emphasis means suppresses the signal amplitude by a signal suppression degree defined by the mode signal, and the signal suppression degree in each mode signal is set either equal or greater as compared with the corresponding signal suppression degree.   
     
     
       8. A video signal coding and decoding apparatus, comprising: emphasis means, having a nonlinear characteristic for increasing degree of signal enhancement of said video signal as amplitude of said video signal decreases, and for setting degree of signal enhancement at a desired level and for generating an output signal,   coding means for generating a code row by compression coding the output signal from the emphasis means   decoding means for decoding the code row and for generating a decoded video signal, and   de-emphasis means having a nonlinear characteristic for increasing degree of signal suppression of said decoded video signal as amplitude of said decoded video signal decreases, and for reproducing said video signal by suppressing the decoded video signal,   means for detecting a DC level of video signal for a specific period; and   mode changeover means for issuing a mode signal by selecting one of L modes, L being a natural number larger than one, depending on the DC level;   whereby the signal enhancement degree of the emphasis means is defined by the mode signal.   
     
     
       9. A video signal coding and decoding apparatus, comprising: emphasis means, having a nonlinear characteristic for increasing degree of signal enhancement of said video signal as amplitude of said video signal decreases, and for setting degree of signal enhancement at a desired level and for generating an output signal,   coding means for generating a code row by compression coding the output signal from the emphasis means   decoding means for decoding the code row and for generating a decoded video signal, and   de-emphasis means having a nonlinear characteristic for increasing degree of signal suppression of said decoded video signal as amplitude of said decoded video signal decreases, and for reproducing said video signal by suppressing the decoded video signal, wherein the video signal contains three component signals; and   the coding and decoding apparatus further comprises:   mode changeover means for issuing at least one different mode signal to the component signals S1, S2 and S3;   whereby the signal enhancement degree of the emphasis means is defined by the mode signal.   
     
     
       10. A video signal coding and decoding apparatus, comprising: emphasis means, having a nonlinear characteristic for increasing degree of signal enhancement of said video signal as amplitude of said video signal decreases, and for setting degree of signal enhancement at a desired level and for generating an output signal,   coding means for generating a code row by compression coding the output signal from the emphasis means   decoding means for decoding the code row and for generating a decoded video signal, and   de-emphasis means having a nonlinear characteristic for increasing degree of signal suppression of said decoded video signal as amplitude of said decoded video signal decreases, and for reproducing said video signal by suppressing the decoded video signal, wherein the coding means codes at a coding compression rate corresponding to plural compression rate control signals, and comprises   mode changeover means for issuing at least one different mode signal to the plural compression rate control signals;   whereby the signal enhancement degree of the emphasis means is defined by the mode signal.   
     
     
       11. A video signal coding and decoding apparatus, comprising: emphasis means, having a nonlinear characteristic for increasing degree of signal enhancement of said video signal as amplitude of said video signal decreases, and for setting degree of signal enhancement at a desired level and for generating an output signal,   coding means for generating a code row by compression coding the output signal from the emphasis means   decoding means for decoding the code row and for generating a decoded video signal, and   de-emphasis means having a nonlinear characteristic for increasing degree of signal suppression of said decoded video signal as amplitude of said decoded video signal decreases, and for reproducing said video signal by suppressing the decoded video signal, further comprising:   mode changeover means for issuing different mode signals corresponding to a reloadable recording medium and a play-only recording medium;   whereby the signal enhancement degree of the emphasis means is defined by the mode signal.   
     
     
       12. A video signal coding and decoding apparatus, comprising: emphasis means, having a nonlinear characteristic for increasing degree of signal enhancement of said video signal as amplitude of said video signal decreases, and for setting degree of signal enhancement at a desired level and for generating an output signal,   coding means for generating a code row by compression coding the output signal from the emphasis means   decoding means for decoding the code row and for generating a decoded video signal, and   de-emphasis means having a nonlinear characteristic for increasing degree of signal suppression of said decoded video signal as amplitude of said decoded video signal decreases, and for reproducing said video signal by suppressing the decoded video signal, further comprising:   means for detecting a spatial correlation of the video signal for a specific period; and   mode changeover means or issuing a mode signal by selecting one mode from L modes wherein L is a natural number greater than one depending on the spatial correlation;   whereby the signal enhancement degree of the emphasis means is defined by the mode signal.   
     
     
       13. A video signal coding and decoding apparatus, comprising: emphasis means, having a nonlinear characteristic for increasing degree of signal enhancement of said video signal as amplitude of said video signal decreases, and for setting degree of signal enhancement at a desired level and for generating an output signal,   coding means for generating a code row by compression coding the output signal from the emphasis means   decoding means for decoding the code row and for generating a decoded video signal, and   de-emphasis means having a nonlinear characteristic for increasing degree of signal suppression of said decoded video signal as amplitude of said decoded video signal decreases, and for reproducing said video signal by suppressing the decoded video signal, further comprising:   means for detecting a time correlation of the input signal for a specific period; and   mode changeover means for issuing a mode signal by selecting one mode from L modes wherein L is a natural number greater than one depending on the time correlation;   whereby the signal enhancement degree of the emphasis means is defined by the mode signal.   
     
     
       14. A video signal coding and decoding apparatus, comprising: emphasis means, having a nonlinear characteristic for increasing degree of signal enhancement of said video signal as amplitude of said video signal decreases, and for setting degree of signal enhancement at a desired level and for generating an output signal,   coding means for generating a code row by compression coding the output signal from the emphasis means   decoding means for decoding the code row and for generating a decoded video signal, and   de-emphasis means having a nonlinear characteristic for increasing degree of signal suppression of said decoded video signal as amplitude of said decoded video signal decreases, and for reproducing said video signal by suppressing the decoded video signal, further comprising:   means for detecting an amount of coding distortion generated by said coding means; and   mode changeover means for issuing a mode signal by selecting one mode out of L modes wherein L is a natural number greater than one depending on the coding distortion;   whereby the signal enhancement degree of the emphasis means is defined by the mode signal.   
     
     
       15. A video signal coding apparatus comprising: emphasis means for enhancing said video signal by a specified enhancement degree and outputting an enhanced video signal;   coding means for compression coding and said enhanced video signal to produce a code stream representing a compression coded video signal; and   decoding apparatus including de-emphasis means for suppressing said video signal,   wherein said specified enhancement degree is smaller than a suppression degree of said de-emphasis means in said decoding apparatus.   
     
     
       16. A video signal coding and decoding apparatus comprising: emphasis means for enhancing said video signal by a specified enhancement degree and outputting an enhanced video signal;   coding means for compression coding said enhanced video signal to produce a code stream representing a compression coded video signal;   decoding means for decoding said code stream and producing a decoded video signal; and   de-emphasis means for producing an output video signal by suppressing said decoded video signal by a suppression degree larger than said specified enhancement degree of said emphasis means.   
     
     
       17. A video signal coding and decoding apparatus comprising: emphasis means having a nonlinear characteristic of increasing an enhancement degree as amplitude of said video signal decreases, and for enhancing said video signal by said nonlinear characteristic of said enhancement degree, and outputting an enhanced video signal, wherein said nonlinear characteristic of said enhancement degree is settable to a predetermined characteristic;   coding means for compression coding said enhanced video signal to produce a code stream representing a compression coded video signal;   decoding means for decoding said code stream and producing a decoded video signal, and   de-emphasis means having a nonlinear characteristic of increasing a suppression degree as amplitude of an input signal decreases, and for suppressing said decoded video signal by said nonlinear characteristic of said suppression degree, and reproducing an output video signal, wherein said de-emphasis means varies suppression degree with respect to said enhancement degree of said emphasis means, and has said suppression degree larger than said enhancement degree of said emphasis means.   
     
     
       18. A video signal reproducing process apparatus comprising: means for producing a decoded video signal by decoding a code stream representing a compression coded video signal; and   de-emphasis means having a nonlinear characteristic of increasing a signal suppression degree as amplitude of said decoded video signal becomes small, and for suppressing said decoded signal in a complementary relation to signal enhancement, or suppressing said decoded signal by a greater suppression degree than a enhancement degree in a signal enhancement, when said code stream is produced by compression coding process after signal enhancement.   
     
     
       19. An optical disk in which a code stream produced by a digital video signal coding and recording apparatus is recorded, wherein said coding and recording apparatus comprises: emphasis means having a nonlinear characteristic increasing in a signal enhancement degree as amplitude of an input video signal becomes small, and for enhancing said input video signal by said nonlinear characteristic of said signal enhancement degree, and outputting said enhanced video signal;   coding means for compression coding said enhanced video signal to produce said code stream, wherein said code stream represents a compression coded video signal; and   laser beam recording means for recording said code stream on said optical disk.